In recent years, high-density ink jet heads that are produced by using a so-called “transfer process” have been proposed in the art, as disclosed in, for example, Japanese Laid-Open Patent Publication No. 10-286953. A transfer process is an advantageous process as a method for producing a high-density head. A method for producing a head using a transfer process is as follows, for example.
First, a separate electrode is formed on a single crystal MgO substrate. Then, a piezoelectric member, being a perovskite-type dielectric thin film made of PZT, is formed on the separate electrode. Furthermore, a vibration plate that functions also as a common electrode is formed on the piezoelectric member by a sputtering method, or the like. Thus, a thin film actuator is produced. Then, the actuator on the substrate is attached to a pressure chamber plate, and the whole or part of the substrate is thereafter removed.
However, it was difficult to produce a line type ink jet head with the transfer process as described above for the following reasons.
In a line type ink jet head, the length of the head in the longitudinal direction needs to be greater than the paper width of the recording paper. For example, in order to record information on A4-size paper, the length of the head in the longitudinal direction needs to be 210 mm or more. Therefore, the length of the single crystal MgO substrate also needs to be 210 mm or more. However, while a single crystal MgO substrate is produced from a rock lump of MgO, the entire rock lump cannot be used, but what can actually be used is only a portion thereof. Therefore, in order to produce a single crystal MgO substrate whose length is 210 mm or more, it is necessary to provide a lump of MgO of such a length, thereby requiring very large equipment. Even if such a single crystal MgO substrate can be produced, the yield will be poor. Therefore, such a substrate will be a very costly material.
Moreover, in a transfer process, it is necessary to deposit, by a sputtering method, or the like, PZT on a single crystal MgO substrate. However, it requires very large equipment to deposit PZT over a large area. In addition, the yield lowers when one attempts to obtain a film that is uniform in properties such as the piezoelectric property and the thickness and that has no crack therein. Therefore, the manufacturing cost becomes very high.
For the reasons as described above, it was difficult to use a transfer process for a conventional line type ink jet head in view of the quality and the cost.
Moreover, along with the increase in the density of ink jet heads, there is an increasing demand for improving the reliability thereof. In the prior art, inspection of an ink jet head including actuators is performed after transferring the actuators onto a pressure chamber block.
With the conventional method, however, when a defect was included in an actuator, it was necessary to waste the pressure chamber block along with the actuator even if the pressure chamber block itself had no problem. In other words, it was not possible to waste only the actuator while using the non-defective pressure chamber block.
The present inventors have devised a way of effectively using a transfer process for a line type ink jet head, in which a plurality of actuators are provided for each pressure chamber block by dividing an actuator, which was a single component in the prior art, into a plurality of actuators. In such an ink jet head using a plurality of actuators, even if a defect is included in one actuator, the other actuators may be non-defective. If inspection is performed after transferring the actuators onto the pressure chamber block as in the prior art, the actuators cannot be wasted individually, whereby it is necessary to waste non-defective actuators along with defective actuators. However, this leads to an increase in the material cost and the manufacturing cost. It also lowers the yield. In view of this, it is preferred to perform an early inspection on individual actuators before they are transferred onto the pressure chamber block, and to waste the defective actuators individually.
Moreover, an ink jet head including a plurality of nozzles, a plurality of pressure chambers respectively communicated to the nozzles, and an actuator for pressurizing or depressurizing an ink in each pressure chamber so as to discharge the ink through each nozzle, has been widely used in the prior art in a recording apparatus such as a printer. In such an ink jet head, the nozzles are arranged in a direction perpendicular to the scanning direction at a minute pitch that corresponds to a predetermined dot density.
In recent years, however, the recording image quality has been improved, and the actuators and the nozzles are arranged with an increasing density. For example, in an ink jet head for recording information at 600 dpi, the nozzles are arranged at a minute pitch of 42.3 μm.
However, as the density of actuators and nozzles increases, it becomes more difficult to ensure uniformity in the properties of the actuators and to process the nozzles properly. If the properties are not uniform among the actuators or if the nozzles are misshaped, it is no longer possible to discharge a predetermined amount of ink droplets through the nozzles and to stably form ink dots of a predetermined size on the recording medium. Therefore, along with the increase in the density, there is a higher possibility that some of the large number of actuators and nozzles may be incapable of forming an ink dot of the predetermined size.
For example, where some actuators have an inferior performance, such actuators can only form ink dots that are slightly smaller than the predetermined size. Such small dots, if dispersed, cannot be distinguished by human eyes. However, if small dots D2 are aligned in a continuous single row, as illustrated in FIG. 45, the difference thereof with respect to normal dots D1 becomes conspicuous. Specifically, if the small dots D2 are aligned in a single row, a linear space that is larger than normal appears between the small dots D2 and the dots D1 of the normal size, resulting in a white streak L1. The so-called “white streak” L1 may lower the quality of character-printing or image-printing.